Want to burn more fat when you work out? Exercise in the morning before you eat, says a new, small study conducted on men. Some weight-loss experts have believed for a while that exercising on an empty stomach can increase fat loss, but this is the first study to show that working out hungry doesn't cause people to eat more later in the day. In fact, researchers found that those who ran on an empty stomach burned almost 20 percent more fat compared with those who had eaten prior to jogging. But researchers say you should ease into the routine. "If you're not used to working out hungry in the morning, start with shorter sessions, building up from 20 minutes to one hour," recommends study author Javier Gonzalez.